The Portland office of the American Red Cross is looking for blood donors to help prevent summer shortages.

While donors with all types of blood are being encouraged to give blood, the Red Cross is specifically seeking those with types O negative, B negative and A negative.

Type O negative is sought because it is universal and can likely be transfused to anyone. A negative and B negative can be transfused to patients with either Rh positive or negative blood. These blood types are the most in demand and the first to run out if there is a shortage.

To encourage donations, the organization is giving away Red Cross T-shirts between June 30 through July 7 while supplies last. To make an appointment to donate blood, visit redcrossblood.org or call 1-800-RED CROSS (1-800-733-2767).